Air raid warning siren



Sept. 7, 1954 w, DESMQND 2,688,302

AIR RAID WARNING SIREN Filed March 9, 1953 I 4 k 23 24 2 22 a PatentedSept. 7, 1954 UNITED STATES PATENT OFFICE AIR RAID WARNING SIREN WilliamF. Desmond, Oak Park, Ill. Application March 9, 1953, Serial No. 341,065

7 Claims. 1

This invention relates to improvements in sirens of the air raid warningtype and refers particularly to a siren characterized by having anemphasized low pitch tone of predetermined frequency.

In producing audible warning signals which are intended to be heard overconsiderable areas, usually heavily built, populous areas, such asintended with air raid warning sirens, a low pitch component of the toneproduced is of advantage. In the first place, the normal noises producedin business offices, banks, manufacturing plants, homes and the like areusually of relatively high pitch and, hence, a warning signal ofrelatively high pitch is frequently lost in the normal noise and at bestis not as attention-arresting as a low tone foreign to the normalnoises. Hence, a signal of relatively low pitch gain attention where ahigh pitch signal may be lost or ignored. secondly, low pitch sounds areof relatively long wave length and, hence, in heavily built areas, soundshadows and dissipation of the wave energy are less likely to occur.

One of the features of the present invention resides in a siren or thelike which produce an attention-arresting signal having a component oflow pitch, the low pitch component being a beat note secured by a pairof sound producing members producing relative high pitch sounds ofdifferent frequencies, the best note resulting from the interference ofthe high frequency signals, and having a frequency equal to thedifference in frequency of the high pitch tones.

Another important feature of the'invention reside in the provision in asiren of a chamber attuned to the frequency of a low pitched beat notewherein a siren is obtained which produces two relatively high pitchedtones with an emphasized low pitch tone.

Other objects and advantages of my invention will be apparent from theaccompanying drawing and following detailed description.

In the drawing, Fig. 1 is a. sectional view, partially diagrammatic,through my improved siren.

Fig. 2 is a transverse sectional view taken on line 2-2 of Fig. 1.

R ferring in detail to the drawing, I indicates a housing which, forconvenience, is divided into three zones, a resonating chamber 2, andfluid pressure chambers 3 and 4. As will be apparent as the descriptionof theinvention proceeds the zones 2, 3 and 4 need not necessarily becontained in a unitary housing, but for purposes of compactness this isthe preferred embodiment of the invention.

An electric motor 5 is positioned in the zone 3 being carried by bracket6 which may be secured to one of the walls of the housing. A rotor I ismounted upon shaft 8 of motor 5 whereby said rotor may be rotated by themotor. The rotor 1 comprises a plurality of radially extending vanes 9each of which terminates at its outer extremity in an arcuate valveplate Ii] which conforms with the inner circumference of the upperportion of that portion of the housing which defines zone 3.

In the zone 4 an electric motor I I i positioned being carried bybracket l2 which, in turn, is mounted upon one of the housing walls. Theshaft l3 of motor II carries a rotor I4 which, similar to rotor 1,comprises radial vanes I5 which terminate in arcuate valve plates IS.

Wall I! which defines a portion of zone 3 and a portion of zone 2 isprovided with an opening l8, and wall I9 which defines a portion of zone4 and a portion of zone 2 is provided with a similar opening 20. It canreadily be seen that openings I8 and 20, respectively, providecommunications between zones 2 and 3, and 2 and 4 adjacent an end ofzone 2.

It will be noted that valve plates II] of rotor 9 move adjacent openingI8 and, in similar manner, valve plates I6 move adjacent opening 20,when the respective motors 5 and II are energized. It will also be notedthat the angular spacings of the vanes 9 and I5, respectively, are such,with respect to the circumferential lengths of the valve plates It! andIE, that the openings l8 and 20 are alternately closed and openedrespectively by the valve plates Ill and l 6. Thus, communicationbetween zones 3 and zone 2 is alternately opened and closed andcommunication between zones 4 and 2 is alternately opened and closed asthe respective rotors I and M are rotated.

In the form of sound producing agency illustrated and described fluidunder pressure such as air, steam or other ga is introduced into bothzones 3 and 4. To accomplish conveniently this end a header 2| connectedto a suitable source of fluid under pressure (not shown) may connectinto delivery pipes 22 and 23 which open, respectively, in zones 3' and4. Thus, both zones 3 and 4, during operation of the device may befilled with fluid under pressure.

In a well known manner the escape of the fluid under pressure throughopenings I8 and 20 with the alternate interruptions by the valve platesI0 and It, respectively, produces a sound characteristic of that knownto be produced by a siren.

As a feature of the present invention, the pitches of the tone producedby the arrangement contained in zone 3 and the arrangement contained inzone 4 are specifically different. This may be accomplished in any wellknown manner, as by rotating one rotor faster than the other if therotors are the same; providing a different number of valve plates oneach rotor, if the motors rotate at the same speed; supplying fluidunder different pressures to zones 3 and ii or using fluids of differentdensities in said zones. The purpose of so producing tones of differentpitch is to cause interference between the sounds such as to create anaudible beat note adjacent the openings I8 and 26 at the open end ofchamber 2.

It is Well known that audible beat notes may be created where thedifference between the wave length of one tone and the wave length ofanother tone in interference with the first tone comprises a tone whosewave length is in the audible range. Hence, the sound produced by mysiren comprises a complex sound produced by the fundamental of rotor land the fundamental of rotor 14 together with a beat note of a wavelength comprising the difference between the two fundamental wavelengths. I contemplate the production of a relatively high pitchedaudible tone by rotor l and a relatively high pitched audible tone byrotor M, the wave lengths or frequencies, however, being different, butsufficiently close to produce a beat note or tone of relatively longwave length or low frequency. The wave length of the beat note or toneis sufficiently high, however, that the waves coalesce to form a tone ofdefinite pitch but is not so high as to fall within the range of thewave lengths of the average noises of ofiices, home, street noises, etc.

To cause the Waves of the beat note to coalesce and produce a tone ofdefinite pitch the frequency of said note or tone is preferably aboveabout 20 cycles per second. Below 20 cycles per second no definitepitched tone is discernible. For use in towns and cities whererelatively high buildings, narrow streets, closed ofiices, andrelatively high pitched sounds are prevalent, an upper limit of thefrequency of the beat note or tone of about '75 cycles per second ispreferred. If higher frequencies than 75 cycles per second are used in asitus of this character, definite sound shadows are produced, that is,the sound waves are not sufficiently long to render the beat tonematerially more effective than the relatively high pitched fundamentaltones directly produced by the rotors.

As an example, rotor 1 may be so driven or may be of such character thata tone of 3600 cycles per second is produced. Rotor 14 may be so drivenor of such character as to produce a tone of 3660 cycles per second. Abeat note will thereby be produced in the compartment 2, adjacent itsopen end where the major interference will occur, of 60 cycles persecond, that is, the difference between the frequencies of the twofundamentals 3600 and 3660. A beat frequency of this character willproduce a definite tone, as opposed to a sound disturbance whereincoalesence does not take place and will be sufiiciently long in wavelength not to be blocked oif by the usual obstructions encountered in atown or city. In addition, the tone will be sufficiently below theaverage noises in pitch that it will be distinctive andattention-arresting.

Of course, it is to be understood that the present invention is not tobe limited to the example set forth hereinbefore since higher frequencybeat tones may be satisfactory or lower frequency beat tones may benecessary depending upon the nature of the obstructions or the nature ofthe normal noise frequencies.

As another important feature of the present invention my sirencontemplates means for emphasizing the beat note or beat tone whereby itwill be augmented and amplified to make it an effective component of thecomplex sound issuing from the siren. As has been hereinbeforedescribed, the major interference between the sound waves produced bythe two fundamental components occurs adjacent the open end of thecompartment 2. I propose to close the compartment 2, as at 24, and thedistance between the closure at 24 and substantially the open end of thecompartment 2, proper, is made substantially equal to one-quarter of thelength of the wave of the beat note or beat tone produced. That is, theclosure 24 is substantially one-quarter wave length from the point wherethe major interference between the fundamental tones is produced.

In this fashion a siren or audible signal is produced comprisingsubstantially three components, the two relatively short wave lengthsounds of the fundamentals and the emphasized relatively long wavelength sound of the beat note or tone.

It is to be understood, of couse, that in some environments, such as, inrelatively flat open country or over water, a higher frequency beat noteor tone than 75 cycles per second may be satisfactory where said beatnote or tone is emphasized as herein described by the use of theresonating chamber. However, for use in congested areas a beat note ortone below 75 cycles per second is preferred.

The frequency of the two fundamental tones may be selected, as desired,within the audible range so long as their differences produce thedesired beat note or tone.

Although a pressure type siren is shown and described, it is to beunderstood that the present invention is independent of the specificmanner in which the fundamental or interfering tones are produced solong as the closed end of the resonating chamber is a distance of aboutonequarter wave length from the point at which the major interference ofthe fundamental tones occur. In addition, if desired, a trumpet portion25, such as an exponential horn may be employed at the open end of theresonating compartment 2.

I claim as my invention:

1. An air raid siren comprising a sound-producing member for producing asound of predetermined relatively high frequency, a secondsound-producing member for producing a sound of relatively highfrequency but of a frequency different from the frequency produced bysaid first sound-producing member, means for simultaneously operatingsaid sound-producing members, said sound-producing members beingdisposed adjacent eachother to cause interference between the twoproduced sound waves and create an audible beat note of relatively lowfrequency, and a closed-end resonating chamber disposed adjacent saidtwo sound-producing members and attuned to the frequency of said beatnote to emphasize said relatively low frequency beat note.

2. An air raid siren comprising a sound-producing member for producing asound of predetermined relatively high frequency, a secondsound-producing member for producing a sound of relatively highfrequency but of a frequency different from the frequency producedby-said first sound-producing member, means for simultaneously operatingsaid sound-producing members, said sound-producing members beingdisposed adjacent each other to cause interference between the twoproduced sound waves and create an audible beat note of relatively lowfrequency, and a chamber having a closed end which is at a distance fromthe zone of major interference between said two relatively highfrequency sounds equal to substantially onequarter wave length of thebeat note caused by said interference.

3. An air raid siren comprising a chamber having a closed end and anopposite open end, means for producing a sound of predeterminedrelatively high frequency adjacent the open end of said chamber,separate means for producing a second sound of relatively high frequencyadjacent the open end of said chamber, means for simultaneouslyoperating said sound-producing means, said two sound frequenciesdiffering from each other by a frequency of relatively low order wherebyinterference takes place adjacent the open end of said chamber and anaudible beat note is created of relatively low frequency, the distanceof the zone of major interference between said relatively high frequencysounds adjacent the open end of said chamber to the closed end of thechamber being substantially equal to one-quarter of the wave length ofthe beat note.

4. An audible signal producing device comprising a housing, meanscarried by said housing for producing a sound of relatively highfrequency, separate means carried by said housing for producing a soundof a frequency difiering from said first mentioned sound by about 75 to20 cycles per second, means for simultaneously operating saidsound-producing means, said two sound producing means being disposedadjacent each other to cause interference between the respective soundsto create an audible beat note of a frequency of about '75 to 20 cyclesper second.

5. An audible signal producing device comprising a housing, meanscarried by said housing for producing a sound of relatively highfrequency, separate means carried by said housing for producing a soundof a frequency differing from said first mentioned sound by about 75 to20 cycles per second, means for simultaneously operating saidsound-producing means, said two sound producing means being disposedadjacent each other to cause interference between the respective soundsto create an audible coalescent beat note of a frequency of about to 20cycles per second, and a resonating chamber carried by said housing forsaid beat note.

6. An audible signal producing device comprising a housing, meanscarried by said housing for producing a sound of relatively highfrequency, separate means carried by said housing for producing a soundof a frequency differing from said first mentioned sound by about 75 to20 cycles per second, means for simultaneously operating saidsound-producing means, said two sound producing means being disposedadjacent each other to cause interference between the respective soundsto create an audible beat note of a frequency of about 75 to 20 cyclesper second, and a resonating chamber carried by said housing, saidresonating chamber having side walls and a closed end, said closed endbeing at a distance from the zone of major interference between saidrelatively high frequency tones equal to substantially one-quarter wavelength of the beat note produced by such interference.

7. An audible signal-producing device comprising a housing, parallelpartition walls in said housing dividing said housing into threechambers, means for simultaneously producing an audible sound ofrelatively high frequncy in each of two chambers, each of said partitionwalls being provided with an aperture adjacent corresponding ends ofsaid walls through which said high frequency sounds issue into saidthird chamber, said sounds of relatively high frequency havingfrequencies differing from each other by a predetermined amount wherebyinterference betweensaid sounds occurs and an audible beat tone ofrelatively low frequency is produced in said third chamber adjacent theend thereof into which said high frequency sounds issue, said thirdchamber having an open end adjacent the apertured ends of said partitionwalls, a closure for the opposite end of said third chamber, saidclosure being at a distance from the open end thereof substantiallyequal to one-quarter wave length of the beat tone.

References Cited in the file of this patent FOREIGN PATENTS Number

